Device for handling of cables on seismic vessels

ABSTRACT

A device to facilitate the handling, maintenance and replacement of seismic equipment and seismic energy sources in the gun arrangement section, i.e. the gun array of seismic gun cables on seismic survey vessels, on the vessel&#39;s after deck (1) by which the gun cables are transferred, with the arrays stored on the deck hanging in suspension rails (6), wherein the cable is wound up on to a number of drums (3) and deployed or recovered from the water over a slip (4) at the after end of the ship. On the deck there are also winch drums (5) for streamer cables. The gun cable drums (3) are placed in a row alongside one another athwartships. Also provided is a row of parallel tracks (6), suspended on rails which can be moved in a crosswise direction. The ends of the rails or tracks (6) are equipped with devices whereby they can be connected to transfer tracks (7) on the slip (4). The gun arrays in their tracks (6) can be moved athwartships, thus providing more working space and allowing better use to be made of the area available on the after deck.

BACKGROUND OF THE INVENTION

The invention concerns a device for handling of cables on seismicvessels on the vessel's after deck, especially the gun arrangementsections, i.e. the gun arrays of gun cables, whereby several gun cablesare transferred and stored on the deck, hanging on suspension rails,while the inner section of the cables is wound on to winding drums,where a slip is arranged for deployment/recovery of the cables into/outof the water and where in addition there are normally winch drums forstreamer cables on the deck.

The gun arrangement section of the gun cable is usually called a gunarray. This term will be used in the following to describe the guncable's gun arrangement section.

At the present time most seismic surveys at sea are conducted usingspecially built ships whose after decks are designed for storing andhandling the seismic gun cables and detection cables or streamer cables,which constitute the means whereby the seismic surveys are performed.The gun array comprises groups of seismic energy sources which transmitpulses into the water, the reflections from these being intercepted bythe detection cables or streamer cables which transmit the signals backto the vessel for processing. Developments in survey methods in recentyears have led to the situation where behind the vessel there are nowtowed a number of gun cables with gun arrays in parallel alongside oneanother, and several streamer cables are also used for the reception ofthe reflection signals. The design and construction of the individualelements have also been under constant development in order to improvethe signal quality and to increase the vessel's productivity. Thisdevelopment has led to an increase in the amount of equipment, resultingin major problems on board the seismic vessels where, due to thedimensions of this equipment, the available space has becomeprogressively smaller. There is a constant need for maintenance work onthe gun arrays, and in addition the gun arrays often have to bereconstructed. There is therefore a great need for improvement in thehandling routines and above all in the storage and working facilities onboard the vessel.

BRIEF SUMMARY OF THE INVENTION

The object of the present invention is to provide a solution to theseproblems.

This object is achieved by the invention with a device of the typementioned in the introduction, which is characterized by the features inthe claims presented.

A natural solution to lack of space on the after deck of a vessel wouldbe to increase the size of the deck and, e.g., to use wider vessels.However, this would be most disadvantageous since the vessel's totaldimensions would thereby be increased disproportionally, substantiallygreater operating expenses would be incurred and the cost of buildingsuch ships would also be significantly greater. An extension of theship's length will not entail any improvement since the cables have tobe deployed into the water from the stern area. Another major problemhas been the positioning of the winch drums for the streamer cables,which have traditionally been placed right at the after-end of the deck.These have occupied a disproportionate amount of space athwartships,thus making it difficult to move the gun cable past them and leading toa limit on the number of cables for which there was room. At the sametime this arrangement has resulted in large areas of dead space behindthe streamer drum, space which it has been possible to use as stowagespace, but which has not been able to be used for handling of cables andmaintenance work. In order to make the best-possible use of the space, apartial solution has been to guide the gun arrays in tracks which arearranged between the streamer drum and the ship's sides, a procedurewhich has led to the equipment in the deployment/recovery area right atthe after end being packed tightly together. One alternative has alsobeen to move the streamer drum to another deck, but this has not been asuitable solution either.

The invention overcomes the above problems by providing a device on awork and after deck of a seismic vessel for handling seismic gun cables,especially gun arrangement sections, i.e. gun arrays and gun cables,several gun cables being transferred and stored on the deck by hangingin suspension rails and wound on winding drums, where there is arrangeda slip for deployment/recovery of the cables into/out of the water andwhere in addition there are normally winch drums for streamer cables onthe deck, characterized in that the cable drums are placed alongside oneanother in a row athwartships, that the gun arrays are guided in a rowof parallel tracks and suspended in rails which can be moved in acrosswise direction, and that the ends of the rails are equipped withdevices for connecting the rail tracks to transfer tracks on the slipfor deployment and recovery of the gun cables.

With the device in accordance with the invention the applicant hassucceeded in providing the opportunity for a considerably more rationalhandling of the equipment. This is achieved by simple means and resultsin the possibility of using the whole area available on the after deckto a much greater extent than previously. Thereby the gun arrays inparticular can be positioned in such a way that maintenance work andreplacement can be carried out without any trouble and the gun arrayscan also be positioned to give a clear space around the gun array(s) onwhich work is being done, so as to give a substantial improvement in theworking conditions. At the same time it succeeds in maintaining thestreamer drums in a favorable position so that the streamer can bedeployed just as easily as before.

The device in accordance with the invention even makes it possible fornarrower ships than before to be used, despite having more spaceavailable on the after deck. The design according to the invention isclearly significant not only with regard to the ship's propulsion in thewater, but also because it will be easier to maintain a large open spaceon the after deck which offers the opportunity of using the device inaccordance with the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference to theaccompanying drawings of two embodiments wherein:

FIG. 1 is a schematic top plan view of a first embodiment of the deviceaccording to the invention on the after deck of a seismic vessel;

FIG. 2 is an alternative embodiment to the device of FIG. 1;

FIG. 3 is a schematic perspective view of a conventional knownarrangement of support rails and movable rails supported on the supportrails;

FIG. 4 is a schematic elevational view of a part of a transfer track fordeploying and recovering seismic gun cables; and

FIG. 5 is a partial schematic view similar to FIG. 2 showing amodification thereof.

DETAILED DESCRIPTION

In the embodiments illustrated in the drawing only the specialprinciples of the design of the invention are illustrated, with noconsideration being given to the ship's design, the actual shape of theafter deck, the shape of the drums or the suspension and the design ofthe various tracks, etc. All these details consist of design featuresand elements which either have been used before on seismic ships or willbe known to a person skilled in the art and can be found used in otherconnections. Thus, e.g., the gun cable drum is of the type which is usedon seismic ships to-day, as are the streamer cable drums and thedeployment/recovery slip at the after end of the ship. In the same waythe guide rails and storage of gun cables will include known elementsfrom seismic vessels, but here modified in order to achieve the deviceaccording to the invention.

The ship's after deck is indicated by 1 and in both principal sketchesis illustrated as a square surface area. The after deck creates a closedspace and is covered by a deck above it, while it is open at the afterend of the ship at 2. In this area the cables are deployed andrecovered. The gun cables are wound on to a number of drums 3 which areplaced alongside one another across ships or athwartships. In the deviceaccording to the invention these drums are placed symmetrically in agroup on the innermost part of the deck. Thus, space is provided for amaximum number of cable drums with winch,.enabling a maximum number ofcables to be kept and stored. Previously cable drums on vessels wereusually placed in two or more groups.

The deployment/recovery of the cables takes place at the after end ofthe ship over a so-called slip which is indicated by 4. The slip can beof any type, and is in principle only a guide for the cable. On thisslip the cables together with the equipment installed on them are guidedinto the water, or on to the deck, in a controlled manner. In theinvention two transfer tracks or rails 7 are placed over the slip and asa part of it in order to guide the cables to the correct passage at thetransition to the water. In the embodiment shown the slip 4 is placedsymmetrically in relation to the cable drums 3, i.e. in the middle ofthe after end of the deck. On each side of the slip 4 a winch drum 5 isarranged for the detector cables or streamers. In the case of normalseismic surveys two streamers will be sufficient, but for extremely widesurveys and in certain constellations, e.g. when several ships are used,more streamers may be required in the water. These will then beinstalled on a deck higher up, even though this is not completelysatisfactory. This will still be a solution for special cases.

The gun cables 10 from the drums 3 with guns 11 suspended thereon in anarray are stored in the deck's longitudinal direction, the cables andgun arrays in the area between the slip 4 and the drums 3 beingsuspended in suitable securing devices, preferably in rails in the roofover the deck. The cable itself is stored on the drums while the arraysection remains in the area. Conventional rail types such as those usedat present and shown in FIG. 3 can be used here or rail sections can beused which form a kind of attachment lug with pulley 12 which keeps thegun cables in position in parallel tracks 6 as illustrated in thedrawing. Thus from every drum 3 there will be a rail or track 6 on whichthe guns 11 with their respective cable 10 are stored ready fordeployment. In the invention these parallel tracks are not, as in priorart, only arranged in those areas which are free at the after end andwhich are not blocked by the streamer drums 5, i.e. in the invention theentire available area has been used, including the area behind thestreamer drums 5, so that all tracks 6 can be arranged in parallel. Thusa correct deployment from the drums 3 is achieved as well as the bestpossible and equal spacing between the gun arrays over their entirelength on deck. This positioning also makes it possible to suspend theattachment devices or rails on the moving element which is placed acrossthe deck or athwartships, since a number of such parallel moving devicesare arranged on the roof. These are then connected with the tracks 6,thus allowing these to be moved in parallel athwartships, i.e. acrossthe deck. This movement will be possible regardless of how thesuspension devices are constructed, either as attachments in the form oftrolleys on crosswise rails 8 or as rails 6 which are supported bytrolleys 13 for movement in parallel on several of the crosswise rails8. In the drawing the crosswise rails or tracks, 8 are illustrated inFIGS. 1 and 2 purely schematically as lines, since the technical designshould be obvious to a person skilled in the art. With such anembodiment all the guns which are suspended on the gun cables in themiddle of the deck will be equally accessible, thus allowing necessarywork to be performed and giving a complete overall view of all theequipment.

When the gun cables 10 with their respective gun array 11--11 have to beplaced in the water or pulled out, a connection is necessary to transferthe cables from rails 6 to the slip's transfer tracks 7. For thispurpose there have been placed in the area between the ends of theparallel rails 6 and the tracks 7 such as shown in FIG. 5 for example,transfer devices which guide the cable in a curved track to the transfertrack. When a cable is deployed, therefore, this transfer device justhas to be "switched" over to the cable which has to be deployed.

The embodiment illustrated in FIG. 2 corresponds in principle to thatillustrated in FIG. 1 and the same reference numbers indicate the sameparts. The difference between the two embodiments is that in theembodiment in FIG. 2 a solution has been chosen in which the suspendedgun cables with respective gun arrays on their tracks 6 can be moved tothe maximum extent out to one or both sides of the ship, thus makingavailable a large open space in the middle behind the slip 4, where thenecessary work can be carried out. The transition from the tracks 6 tothe drums 3 causes no problems, since the cables and the gun arrays areflexible. Here it is possible to pull forward the array or arrays onwhich work requires to be done and thereby be able to work under themost favorable working conditions possible. When the cables and gunarrays are deployed these can be pulled forward in turn until they arein line with the transfer rails 7, whereupon the rails are connectedtogether and the cables guided out over the slip. This embodiment thusprovides an extremely easy transition to the deployment/recovery system.

It should be obvious that a number of modifications would be possiblewithin the scope of the invention. Variants could be employed containingelements from both the embodiment in FIG. 1 and in FIG. 2, and there arealso a great number of variations possible in the suspension system,transition arrangements between the various track parts, etc. All suchmodifications are intended to fall within the scope of the invention.When using the device according to the invention it will be necessaryfor the deck surface 1 to be entirely free of supports, pillars, etc.since the cables should be able to be moved athwartships. Thispossibility is offered and also facilitated due to the fact that thedevice according to the invention enables narrower ships than before tobe used. In the embodiment in FIG. 1 no special instructions areindicated regarding the moving of the tracks 6 athwartships, since theobject here is to achieve the most uniform distribution possible of thecables with the gun arrays in the space available, thus making the bestpossible use of the space. It should, however, be obvious that theproposed suspension will naturally make the most of the opportunitiesfor opening up space between the cables in the tracks 6 when this workis required to be done. Motor power, e.g. of an electrical or hydraulicnature, will preferably be used for moving the gun arrays on the tracksor rails 6, but it will also be possible to perform the moving proceduremanually. Such an alternative will be particularly relevant in theembodiment in FIG. 1, where the tracks or rails 6 only have to be movedaside a little to give room to work, while for moving longer distances,as in FIG. 2, it can be advantageous to use motor power. In order toprevent accidental sliding it will, of course, be possible to lock allrails and movements so that no movement can take place due to heavyseas.

It should be noted that the design of the slip and the design andpositioning of streamer drums do not constitute any part of theinvention. It will be entirely possible to position the slipasymmetrically on one side or to have one slip on each side and guidethe gun cables accordingly, even though the symmetrical arrangement ispreferred. The streamer drums can be positioned accordingly and it mayalso be possible to arrange, e.g. three streamer drums distributedsymmetrically, with slips in the spaces between them.

The arrangement according to the invention will be advantageous even ifno streamer drums are placed on the work deck.

I claim:
 1. In a device on a work and after deck of a seismic vessel for handling cables having seismic gun arrangement sections, including gun arrays and gun cables, said gun cables being transferred and stored on the deck of the vessel, suspension rails on which said gun cables are supported, winding drums on which said gun cables are wound, a slip for deployment and recovery of said gun cables into and out of the water, and winch drums for streamer cables on said deck, the improvement comprising:a plurality of cable-winding drums disposed alongside each other for rotation on parallel axes extending in a transverse direction athwartships; a plurality of transverse support rails mounted on said vessel in said transverse direction in spaced relationship; gun cable support means movably mounted on said transverse rails for supporting and guiding said gun cables in a plurality of parallel tracks movable in said transverse direction; transfer tracks mounted on said slip for transferring said gun cables and gun arrays thereon during said deployment and recovery of said cables into and out of the water; and ends on said gun cable support means adjacent said transfer tracks.
 2. The device as claimed in claim 1 wherein:said gun cable support means comprises support rails for said gun cables movably mounted for displacement transversely toward both sides of said vessel.
 3. The device as claimed in claim 2 wherein:said gun cable support rails are transversely movable separately.
 4. The device as claimed in claim 1 wherein:said gun cable support means comprises gun cable support rails in parallel spaced relationship in said transverse direction athwartships.
 5. The device as claimed in claim 4 wherein:said gun cable support means further comprises load-carrying elements movably mounted on said gun cable support rails for guiding said gun cables, and means for leading said elements onto said transverse support rails.
 6. The device as claimed in claim 1 wherein:said transfer tracks comprise at least two separate transfer tracks in relative spaced relationship in said transverse direction.
 7. The device as claimed in claim 6 wherein:said slip is disposed at the after end of said vessel.
 8. The device as claimed in claim 1 wherein:said streamer cable winch drums are disposed in relative spaced relationship with respect to each other in said transverse direction to provide a central area therebetween; and said slip is disposed in said central area relative to said streamer cable winch drums.
 9. The device as claimed in claim 8 wherein:said slip is disposed at the after end of said vessel.
 10. The device as claimed in claim 1 wherein:said streamer cable winch drums are disposed on each side of said slip in said transverse direction.
 11. The device as claimed in claim 1 wherein:a separate slip is provided adjacent each side of said after deck to provide a space therebetween, and at least one streamer cable winch drum is disposed in said space between said slips.
 12. The device as claimed in claim 11 wherein:said slips are disposed at the after end of said vessel.
 13. The device as claimed in claim 1 wherein:said slip is disposed at the after end of said vessel. 